Magnesium base alloy



Patented June 16, 1942 MAGNESIUM BASE ALLOY John C. McDonald,.Midland,Mich., assignor to The Dow Chemical Company, Midland, Mich-., acorporation of Michigan No Drawing. Application December 23, 1940,Serial No. 371,378

4' Claims.

The invention relates to magnesium base alloys, and more particularlyconcerns an alloy of this nature having a high degree of formabilityassociated with correspondingly high yield and tensile strengths.

Magnesium base alloys are being widely used in the structural arts wherea light weight metal is highly desirable, such as for use in makingcastings, fcrgings, and the like. However, the use of these alloys inthe rolled form to make sheet metal articles requiring formingoperations, such as bending and drawing, has not progressed as rapidlydue to the fact that, in general, alloys having good formability orductility, permitting relatively sharp bends to be made without thearticle developing external cracks, usually have inferiorcharacteristics as regards-their 0.3 per cent of .cerium, and 5 per centof thal-' lium, the balance being magnesium.

The following table, listing some of the properties of rolled sheetmetal made from my new quaternary alloy, and comparing these propertieswith those of closely related ternary alloys,

illustrates the improvement in tensile and yield strengths of my newalloy over similar properties of related alloys.

In the table, the per cent elongation is to be regarded as the measureof ductility or formability of the alloys.

tensile and yield strengths.

It is, accordingly, the principal object of the invention to provide amagnesium base alloy which can be made into rolled sheet and the likepossessing a high degree of ductility or form-' ability at ordinarytemperatures, enabling it to be sharply bent, drawn, or otherwiseshaped, while having high tensile and yield strengths.

Other objects and advantages will be apparent as the description of theinvention proceeds.

My invention resides in the discovery that a magnesium base alloycontaining from about 0.4 to 12 per cent of aluminum, 0.01 to 1 per centof cerium, and from 1 to 15 per cent of thallium possesses theaforementloned'desirable properties. The term magnesium used herein andin the appended claims is intended to include magnesium containing theordinary impurities present in the commercially pure metal, such astraces of iron, nickel, copper, and silicon. While the properties ofhigh tensile and yield strengths, coupled with excellent formability,are manifest over the entire range of composition indicated,

I have found that, in general, compositions DOS-'65 The properties setforth above under the term Lannealed were obtained by first rollingspecimens of the alloys at a temperature of between 450 to 550 F., andthereafter annealing them at various temperatures in a range of from 400to 800 F. The properties selected for the table were those .of theannealed specimens which exhibited the maximum elongation. Theproperties set forth under the term "cold rolled were obtained bysubjecting specimens of the alloys which had first been hot rolled attemperatures of 450 to 550 F. to additional rolling in the cold state.The properties selected for the table were those of the cold rolledspecimens which exhibited the greatest tensile and yield strengths,while having at least a 1 per cent elongation in two inches.

A comparison of the properties listed in the table shows that thecombined properties of my new polynary alloy are superior to those ofthe related alloys. For example, it will be noted that the yield andtensile strengths in the annealed and the cold rolled state show ageneral improvement over similar properties of related alloys, while theper cent elongation, which is to be regarded as a measure of theductility or formability of the alloy, is of a high order, thusrendering the alloy suitable for use in forming operations. Acorresponding improvement is ex,- hibited throughout the compositionrange or alloying ingredients indicated.

While the new alloy is most useful in wrought form due to itsformability characteristics coupled with high strength properties, itmay also be suitably used for making castings, extruded forms, and thelike. It is further pointed out that the new alloy is amenable tosolution and precipitation heat treatments, which, accordingly, modifyits properties.

It has further been discovered that manganese may be added to themagnesium-cerium-aluminum-thallium alloy above described withoutsubstantially altering the formability characteristics. The presence ofthe manganese improves the yield and tensile strengths of the alloy andat the same time improves the corrosion characteristics of the alloy andthus makes its'addition desirable. The following table lists theproperties of rolled sheet made from my new alloy having manganese addedthereto.

Misch-metal. Magnesium-cerium alloys are commonly made up by employingMischmetal as a source of cerium. It is sometimes desirable to add morethan the theoretical amount of Misch-metal, since the alloyingefiiciency is not always 100 per cent and some loss may be intain analloy containing more than 1.0 per cent of manganese. In compositionscontaining more aluminum, such as from 8 to 12 per cent, it is difficultto obtain an alloy containing more than 0.5 per cent of manganese.

It is to be understood that the invention is not to be limited to thespecific composition herein described, but may take other forms withoutdeparting from the scope of the invention.

I claim:

1. A magnesium base alloy containing from 0.4 to 12 per cent ofaluminum, from 0.01 to 1 per cent of cerium, and from 1 to 15 per centof thallium, the balance being magnesium.

It is evident from examination of the properties listed in the tablethat the formability characteristics are not substantially impaired bythe addition of manganese, while the tensile and yield strengths showimprovement over the related alloys without manganese.

The new alloy may be compounded by any of the methods usually employedfor alloying metals with magnesium, such as by adding the alloyingingredients singly or jointly to a bath of molten magnesium, which ispreferably protected from oxidation by a suitable flux. The cerium maybe added to the alloy as such, or in the form of and from 0.01 to 3.0per cent of manganese, the

balance being magnesium.

4. A magnesium base alloy containing 6 per cent of aluminum, 0.3 percent of cerium, and 5 per cent of thallium.

' JOHN C. MCDONALD.

